No self respecting ungulate wants to meet his/her death by some lackluster cartridge.

Rick

Probably not a popular opinion but I have a 40-90 BN that makes quite a hunting rifle. I use Starline 45-2.6" cases and one pass through the 40-90 FL sizer and they are ready.
My rifle has a 1/18" twist so I keep bullet length not much over 1.3" but that gets me very close to 400 grain .   
The 40-90 BN is the fastest BP cartridge I have ever used. My rifle is an imported Sharps 1874 action with a Big Timber C. Sharps barrel. Suits me just fine and I live in Dell, MT which is elk country.

Long ago I was gifted from a hunting client in Alaska a Winchester 1886 in 40-82.  Once I learned that in the 1886 Win the 40-82 was an express cartridge with slow twist rifling I sold the rifle.
Living in Alaska at the time I thought such a heavy rifle in 40 caliber should be able to shoot at least a 400 grain bullet which it would not. Well it would shoot them but the bullets tumbled.
I sold that rifle and bought another basket case 1886 and had a friend re-barrel it to 50 Alaskan with a 1/24" twist. Then I had a real Alaska gun and over time it proved itself a one shot moose rifle.
I loaned it to a fella here in Montana for a buffalo cull of a rouge bull. Again one good shot with that 525gn WFN bullet starting at 1750 fps was plenty to put the big bull down.
  I talked to the processor and he told me the live weight of that bull was 2200 pounds.  He also gave me the recovered bullet a classic mushroom from the BHN-8 alloy I normally use and though I dont remember the weight loss I know it was slight.

Not sure if this is correct, but would think with anything bigger than 40-65 and smokeless powder the only limit is action strength. 

ETA If using black powder go big or go home. 

To clarify my above statement, with 40-65 and bigger cases and smokeless powder. Case capacity is greater than the amount of powder/pressure the action can take. If im wrong and a smokeless load in 40-82 will have higher velocity than 40-65 I would like to know. Still want a 40-82 but didn't think it would do anything my 40-65 would do but look cooler.